Messages in this thread |  | | Date | Thu, 28 Sep 2017 21:34:16 +0200 | From | Andrew Lunn <> | Subject | Re: [PATCH RFC 3/5] Add KSZ8795 switch driver |
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On Mon, Sep 18, 2017 at 08:27:13PM +0000, Tristram.Ha@microchip.com wrote: > > > +/** > > > + * Some counters do not need to be read too often because they are less > > likely > > > + * to increase much. > > > + */ > > > > What does comment mean? Are you caching statistics, and updating > > different values at different rates? > > > > There are 34 counters. In normal case using generic bus I/O or PCI to read them > is very quick, but the switch is mostly accessed using SPI, or even I2C. As the SPI > access is very slow.
How slow is it? The Marvell switches all use MDIO. It is probably a bit faster than I2C, but it is a lot slower than MMIO or PCI.
ethtool -S lan0 takes about 25ms.
No other driver does caching. So i'm hesitant to add one which does.
> These accesses can be getting 1588 PTP timestamps and opening/closing ports.
You could drop the mutex between each statistic read, so allowing something else access to the switch. That should reduce the jitter PTP experiences.
Andrew
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